Electric heating element and wiring therefor



S. L. KELLY. ELECTRICHEAHNG ELEMENT AND WIRING THEREFon. APPLICATION FILED OCT. 23. |916.

Patented Aug, 3, 1920.

INVENTDR UNITED STATES PATENT OFFICE.

Specication of Letters Patent.

Patented Aug. 3, 1920.

Application filed October 23, 1916. Serial No. 127,166.

To all whom 't may concern:

Be it known that I, SHERMAN L. KELLY, a citizen of the United States, and a resident of Toledo, in the county of Lucas and State of Ohio, have invented a certain new and useful lllectric Heating Element and Wiring Therefor; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as Will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawings, and to the characters of reference marked thereon, which form a part of this specification.

This invention relates to electrical heating means, and particularly to heating elements for electric stoves.

In the use of heating elements of this character, considerable trouble has been experienced by reason of, a large portion of the heat generated in the element radiating from the bottom thereof, thereby not only dissipating the heat but also highly heating the parts ca'rr ing the element and causing injury to the lead wires, binding posts and the connection between said posts and the resistance conductors in the element.

An object of my invention is the provision of an element which will reduce to a minimum the dissipation of heat from the under side thereof, thereby conserving the generated heat for cookin or compartment heating purposes and whlch will also prevent an undue heating of the electrical connections and prolong the life and eiiciency thereof.

A further object of my invention is the provision of improved wiring for heating elements whereby the injurious puncturing of the insulation between the heating coils or adjacent conductor strips is prevented when an induced current is set up in 'a coil by reason of a short-circuiting thereof.

The invention is fully described in the following specification, and while, -in its broader aspect, it is capable of embodiment in numerous forms, a preferred embodiment thereof is illustrated in the accompanying drawings, in which- Figure 1 is a central vertical section of a heating element embodying my invention. Fig. 2 is a bottom View of the central portion thereof, with the inclosing protector cup removed` and Figs. 3, 4, 5 and 6 are diagrams, respectively, of the element wiring in connection with a switch set at high heat, medium heat, low heat and off positions, respectively.

Referring to the drawings, 1 designates a metal hot-plate, preferably of iron and having an endless flange 2 depending from its bottom adjacent to its edge to form the bottom of the plate in cup shape, as shown. A boss 3 is also shown as depending from the center of the hot-plate.

An electrical insulating material 4 of plastic form is deposited in and substantially lls the space between the flange 2 and boss 3, and embedded in this are the resistance conductors, which, in the present instance, comprise two coils or conductor strips 6 and 7, arranged, preferably, in spiral form within the insulation with the coils thereof alternating. The insulation 4 `is intended to completely insulate the coils from each other and from the plate 1. The terminals ofthe coils 6 and 7 project from the bottom or under side of the insulation 4 and connect the terminal posts, as hereinafter described.

The hot-plate 1 rests on the top of a panlike member 8, with its flange 2 tting therein, the bottom of said member bein, spaced from the bottom of said plate and rom the insulating material to form a chamber for receiving a heat insulating material 9, which fills such space.`

The member 8 has a central opening in its bottom and inserted into this opening is the inner reduced end of a plug member 10 of electrical insulating material, such for instance, as porcelain. A stem 11 is secured to and projects central openin in the plug. 10 and has a nut 12 threade thereon in enga ement with the outer side of the plug an serving in conjunction with said stem to retain the plate 1, holding-pan 8 and insulating plug 10 in assembled relation. The plug 10 carries and has the terminal posts 13, 14 and 15 projecting a considerable distance outward therefrom in equidistantly spaced relation around the stern 1l as a center, said posts being shorter than said stem, as shown.

In my improved wiring for the heating element, the outer and inner ends of the coils 6 and 7, respectively, are connected together,

being clamped, in the present instance, between a pair of nuts 16 on the post 15, as shown in F ig. 1 and indicated by the line 15 in the wiring diagrams; the inner end of the coil 6 is connected to the post 13 by binding nuts 17 thereon, and the outer end o the coil 7 is attached to the post 14 by binding nuts 18 thereon.

A snap-switch of the multiple circuit type having four stationary contacts 19, 20, 21 and 22 is preferably employed, with the lead-in or line wires 23 and 24 connected to the contacts 19 and 21, respectively.

The contact 19 has a connection 25 with the inner end of the heating coil 6 to which it is connected by the binding nuts 17 on the post 13; the contact 20 has connection 26 with the outer end of the coil 7 through the medium of the post 15 and binding nuts 16. The switch has different sets of moyable contacts, one set comprising the insulatingly spaced bridging pieces 28 and 29, which, when the control member is in a prede termined point of its movement, are adapted to respectively bridge the space between the contacts 19 and 20 and the contacts 21 and 22, as shown in Fig. 3, this connection being desired for high heat pur oses. For medium heat the switch is provi ed with a bridging piece 30, which, when in a predetermined position of its movement, is adapted to make electrical connection between each of the contacts 20, 21 and 22, as shown in Fig. 4. For low heat the switch is provided with a bridging piece 31, which, at a predetermined point in a movement of the control member, is adapted to electrically connect the contacts 20 and 21. When the current is off, a bridging piece 32 in the switch connects the contacts 20 and 22, but has connection with neither line contact 19, 21.

When the switch is in position to close the high heat circuit, as shown in Fig. 3, the side 23 of the line has connection through the Wire 25 with the inner end of the coil 6 and also has connection through the bridging piece 28, contact 20 and wire 26 with the outer end of the coil 7. The other. side 24 of the line has connection through the bridging piece 29, contact 22 and Wire 27 with both the outer end of the coil 6 and the inner end of the coil 7. It is thus evident that when the switch is in this position current will iiow from the lead-in wire 23 to the inner end of the coil 6 through the wire 25; also that a current will iow to the outer end of the coil 7 from said lead-in wire through the bridging piece 28, contact 20 and wire 26, and that the two currents will join and ow out from the coils 6 and 7 through the Wire 27 to the contact 22, thence across the bridging piece 29 to the contact 21 and out through the line wire 24.

When the switch is set for a medium heat, the current will flow from the wire 23 recesses 35 in the side Wall of the shell.

through the Wire 25 to the inner end of the coil 6, thence outward through said coil and through the wire 27 to the contact 22 across the bridging piece 30 to the contact 21, and thence out through the line Wire 24, thus cutting out the coil 7 over the high heat position of tne switch.

When the switch is set for a low heat, as shown in Fig. 5, the current Hows from the wire 23 through the Wire 25 to the inner end of the coil 6 thence outward through said coil to the inner end of the coil 7 and outward through the coil 7 to the wire 26, thence to the contact 20 and across the bridging piece 31 to the contact 21 and lead-out Wire 24.

In heating elements of this character which have heretofore been used, the heating coils, so far as I am aware, have not been connected together as herein illustrated, but on the contrary have had their inner ends connected. Wlth this former arrangement, upon the. short-circuiting of one coil, which occurs when switching from high tov medium heat, the induced current which is set up momentarily in the short-circuited coil Hows in an opposite direction in the wire 27, or its equivalent, from the current passing from the live coil, thus causing a puncturing of the insulation at the point Where the two oppositely moving currents come together. This action only occurs when switching from high to medium heats. By connecting the inner end of the coil 7 to the outer end of the coil 6, the induced current which is set up by a short-circuiting of one coil will in the same direction through the wire 27 as the current from the live coil, as is apparent by reference to the diagrams. It will be understood that the objectionable feature which my particular wiring overpomes is present only in alternating current mes.

When the heating coils have been properly connected with the switch, the terminal posts 12, 14 and 15 are partially inclosed by a shell or cup-like member 33 of insulating material, which has a centrally disposed aperture through which the stem 11 projects and is firmly secured withthe inner side of its bottom resting against the outer ends of said terminal posts by a nut 34 on the outer end portion of the stem 11. The shell 33 is o substantially the same size in diameter as the insulating plug 10 and has the upper end of its side wall terminating in spaced relation to said plug to permit the free circulation of air between the two parts and around the conductor posts and wiring connected thereto. The wires 25, 26 and 27, which connect with the respective posts 13, 14 and 15, project through openings (ir t is thus evident that while the terminal posts and electrical connections therewith are proiiovv tected, they are exposed to the free circulation oi air therearound to prevent heating thereof to any considerable extent.

I wish it understood that while I have described a particular construction of hotlate and wiring therefor, I do not wish to restrict the invention to such specific construction or arrangement of the parts, as it is capable of numerous modifications without departing from the spirit of the claims. Havlng thus described my invention, what I claim as new, and desire to lsecure by Letters Patent, isf 1. In an electric heating element, a line circuit, a switch therein, and a plurality of resistance coils having their convolutions alternating, with the inner end of one coil electrically connected to the outer end of the other coil and in switch connection with one side of the line, and with the other ends of said coils in connection with the other side of the line, one of said last connections through the switch.

2. n an electric heating element, a line circuit, a switch therein, and two resistance coils having their convolutions alternating, with the inner end of one and the outer end of the other coil in electrical connection with one side of the line, with at least one of said connections through said switch, and-with the other ends of said coils in connection with the other side of the line.

3. In an electric heating element, a line circuit, a switch therein, and two resistance coils having their convolutions alternating, with the inner end of one and the outer end of the other coil in electrical connection with one Aside of the line, with at least one of said connections through said switch, and with the other end of one of said coils in switch connection with the other side of the line.

4. In an electric heating element, the combination with a line circuit and a switch disposed therein and having a plurality of contacts, of two conductor coils, with the inner end of one and the outer end of the other electrically connected with one of the switch contacts and with the opposite end of one in permanent electrical connection with one side of the line circuit and with the opposite end of the other in connection with one of the switch contacts, said switch bein operable to close circuits through both o said coils in multiple with the line, to shunt one of said circuits, to connect the coils in series with each other and with the line, and to open the line circuit.

In testimony whereof, I have hereunto signed my name to this s ecification.

SHER AN L. KELLY. 

